This is a short post to reflect on the value of information, especially when testing batteries.
Here is a charging curve on an EV95 battery module. This is a 12V 95Ah module composed of 10 cells.
All seems to look ok. Right? The module charges (with 30A) until it reaches 14.6V, then the voltage goes down a bit indicating that the charge is completed, and then the charge is interrupted by the charger. The rest of the graph is 5 minutes wait period and a short load test with 34A.
Not so fast though... look at the following graph showing the individual voltages of the cells in that module:
It is clearly visible that cell 10 is an outlier and is fully charged long before the rest of the cells. This cell is also the reason for the charge interruption.
It is also visible that the rest of the cells are "all over the map".
I will experiment some more with this module and the question remains - is there such thing as too much information?
Comments (1)
Anonymous
April 09, 2018 at 10:43 PM
possibly the outlier cell is much colder, or the other cells are warmer. this can also be from loose or small terminal connections at the cell. errors injected from test equipment? swap channels around to compare, or put all channels on one cell. The step at 16:50 is rather sudden. Hmm someone didn't tap into this bank between C8 & C9 to get another voltage by chance?
Thanks for sharing.TH